Cement additive

ABSTRACT

A cement additive consisting of calcium sulfate and calcium fluoroaluminate having the chemical formula 3CaO.3Al2O3.CaF2.

United States Patent Mizunuma et a1.

1111 3,856,540 1 51 Dec. 24, 1974 CEMENT ADDITIVE Inventors: Tsutomu Mizunuma; Takeo Yoshida, both of Ohmi, Japan Assignee: Denki Kagaku Kogyo Kabushiki Kaisha, Tokyo, Japan Filed: Jan. 26, 1973 App]. No.: 327,556

Foreign Application Priority Data Jan.28, 1972 Japan 47-10312 US. Cl. 106/89, 106/314 Int. Cl.....- C04b 7/02 Field of Search 106/89, 314, 315

Primary Examiner-Delbert E. Gantz Assistant ExaminerJ0hn P. Sheehan Attorney, Agent, or Firm-Sughrue, Rothwell, Mion, Zinn & Macpeak ABSTRACT consisting of calcium sulfate and roaluminate having the c emica fo rmula 2 Claims, 1 Drawing Figure CEMENT ADDITIVE This invention relates to a cement additive and particularly to a cement additive providing both properties of expansion and strength to a cement by admixing the cement additive to the cement.

Conventional Portland cement has proper ultimate strength and is generally used in the field for setting engineering machines, constructions and molded concomposed of glu m iga e m eg1, gypsum an nd ce:

ment still possesses an insufficient expansion rate. Fur- I I e I ther, a cement expanding agent consisting mainly of a calcium sulfoaluminate series compound is superior to the above expanding system with respect to its expansion properties. However, since free CaO-contained in the calcium sulfoaluminate series expanding agent has a very low resistance to moisture, the expanding agent is weathered and thus the expansivity of the agent decreases considerably.

A cement expanding agent consisting mainly of gypsum possesses strength deficiencies, involves a long aging period, and is still insufficient in the practical use.

The inventors have made investigations in order to obviate these drawbacks and accomplished the present invention.

it is an object of this invention to provide a cement additive which will allow molds to be used three to four times per day instead of once a day in the field of producing molded concrete products.

It is a further object of the present invention to provide a cement additive permitting the rapid working for setting engineering machines and constructions.

Another object of the invention is to provide a cement additive preventing in mortar and concrete which are caused by shrinkage of cement in the hardening and drying.

The present invention consists in a cement additive consisting mainly of a mixture of calcium sulfate and calcium fluoroaluminate having the chemical formula 3CaO'3Al O 'CaF,. The calcium fluoroaluminate is produced by mixing lime, bauxite and fluorspar in such an amount that the mineral of the resulting product becomes 3CaO'3Al,O,-CaF, and burning the resulting mixture at a temperature of l,200-l,400 C.

if the temperature is lower or higher than the above range and the cooling rate of the resulting clinker is not proper, side reactions occur and therefore the desired results are not obtained.

The above ternary compound 3CaO'3Al,O,-CaF, is per se known in the art and has been described by J. K. Leary [Nature, 194(482) (l962)79].

The mixing ratio of the above described calcium fluoroaluminate and calcium sulfate is 80-10% by weight of calcium fluoroaluminate and -90% by weight of calcium sulfate.

When the resulting mixture is combined with conventional Portland cement in an amount of l-30% by weight, the set time of the cement may be shortened in Furthermore, the cement additive may be used together with a dispersing agent, AE agent, water proofing agent, and the like.

Calcium sulfate in accordance with this invention may be used in the form of dihydrate, hemihydrate and anhydrate.

Since the content of free CaO in the cement additive according to the present invention is very low, the deterioration of properties due to weathering hardly occurs, and the additive is stable. Accordingly, the expansion rate of the cement additive is considerably higher than those of the above described cement expanding agents composed of alumina cement and gypsum or of l2CaO-7Al O and gypsum. Another merit of the present invention is that the expansion rate of the cement additive can be regulated by varying the mixing ratio of 3CaO-3A1 O -CaF and calcium sulfate. Moreover, when the cement additive having a high content of 3CaO-3Al O CaF and a low con tent of calcium sulfate is mixed with Portland cement, the strength of the Portland cement can be increased considerably. Accordingly, the cement additive of the present invention can be also used as a strength-improving agent of cement. Moreover, when a mixing ratio of the cement additive to cement is increased or the particle size of the ce- 0 .present invention.

The following examplesare given for the purpose of illustration of this invention and are not intended as limitations thereof.

EXAMPLE I Commercially available calcium carbonate, commercially available alumina and fluorspar were mixed in the following proportions.

k by weight Calcium carbonate (purity 99.0%) 43.8 Alumina (purity 99.5%) 44.3 Fluorspar (purity 95.0%) I 1.9 100.0

The resulting mixture was charged into a platinum Table 3 crucible and burned at l,350 C for 2 hours in an elec- Bending strsngth Compressive strength tric furnace. The resulting clinker was confirmed from (Kg/7cm (Kg/Cm the X-ray analysis curve as shown in the FIGURE that 5 days days days days days days the clinker had a composition of 3CaO-3Al O -CaF 52:35:? 495 793 13! 339 385 Cmenl Chemically analytical value according to 11$ R5202 lS 36] 65.7 H2 295 402 shown in the following Table l.

Table 1 lg-loss SiO, Fe O, 7 0,0 CaO Tio, MgO CaF, Total F-CaO The obtained clinker contained 0.4% by weight of EXAMPLE 3 free CaO. The clinker was mixed with anhydrous calcium sulfate, which was obtained by burning calcium sulfate dihydrate at l,000 C for 1 hour, and the resulting mixture wasground to a specific surface area of 2,930 cmlg to obtain a cement additive. In the above mixing, by weight of the clinker (3CaO*3Al O CaF and 75% by weight of anhydrous calcium sulfate were mixed.

The obtained cement additive and conventional Portland cement were mixed in a weight ratio of l 1% 89% to prepare an enriched cement, and the expansion rate of enriched cement was measured according to 118 A1 125. The measuring method is as follows. The enriched cement and sand were mixed in a weight ratio of l 2 to prepare a mortar, and the mortar was mixed at a water/cement ratio of 65%, formed in a metal mold having a dimension of4 X 4 X 16 cm, cured for one day in a himid air and taken out from the metal mold. The length of the mortar sample was used as a base length. The mortar sample was further cured in water at 20C for the predetermined period of time as shown in the following Table 2, and the length of the sample was compared with the original length,'whereby the expansion rate of the sample was measured. The obtained result is shown in Table 2.

For comparison, the above experiment was repeated, except that l2CaO-7Al O clinker and CaO Al O clinker were used instead of the 3CaO'3Al O 'CaF clinker of the present invention. The obtained results are also shown in Table 2.

Table 2 A cement additive was produced from the 3CaO-3Al- O -CaF clinker obtained in Example 1 and anhydrous calcium sulfate in the same manner as described in Example l, except that 67% by weight of the clinker and 33% by weight of the calcium sulfate were mixed and the mixture was ground to a specific surface area of 5,200 cm /g. The cement additive and conventional Portland cement were mixed in a weight ratio of 30%:70% to prepare an enriched cement. A mortar was prepared in the following compounding proportions.

Enriched cement 520 g San (Toyoura sand) L040 g ater 234 cc The compressive strength of the formed mortar after curing one hour was about Kg/cm and that after curing 1 day was 190 Kglcm As seen from the above Examples, when the cement additive of the present invention, which is composed of calcium fluoroaluminate represented by the chemical formula 3CaO'3Al O 'CaF and calcium sulfate, is mixed with cement, the expansion rate of the resulting cement composition is about to times or more as compared with the case when conventional cement additive is used, and moreover the strength of the cement composition can be increased by about 30% or more. These effects have never been attained by conventional cement additives. Therefore, the present invention is very useful for industry.

Present invention 3CaO.3Al,O,.Cal-,:CaSO,

Conventional additive l2CaO.7Al,O,: CaSO, CaO.Al,O,:CaSO

A cement additive was produced from the 3CaO-3Al- O -CaF clinker obtained in Example 1 and anhydrous calcium sulfate in the same manner as described in Example 1, except that 33% by weight of the clinker and 67% by weight of the calcium sulfate were mixed and the mixture was ground to a specific surface area of 5,200 cm'Ig. The cement additive and conventional Portland cement were mixed in a weight ratio of 7%:93% to prepare a mortar. The result of the strength test of the mortar according to H8 R5201 is shown in the following Table 3 together with the result in the case of mortar of conventional Portland cement alone.

l. A cement additive comprising calcium sulfate from 20 to 90% by weight and calcium fluoroaluminate having the chemical formula 3CaO'3Al,O;,'CaF, from to 10% by weight. 

1. A CEMENT ADDITIVE COMPRISING CALCIUM SULFATE FROM 20 TO 90% BY WEIGHT AND CALCIUM FLUOROALUMINATE HAVING THE CHEMICAL FORMULA 3CAO.3AL2O3.CAF2 FROM 80 TO 10% BY WEIGHT.
 2. A cement composition comprising cement from 99 to 70% by weight and a cement additive from 1 to 30% by weight, said cement additive comprising calcium sulfate from 20 to 90% by weight and calcium fluoroaluminate having the chemical formula 3CaO.3Al2O3.CaF2 from 80 to 10% by weight. 